This invention relates to magnetic bubble memories; and, more particularly, it relates to methods of generating a rotating magnetic field for moving the bubbles from one location to another in such memories.
A bubble memory is comprised of a thin planar film of magnetic material in which bubbles are generated by a magnetic field that points perpendicular to the plane of the film. An insulating layer lies over the thin film of magnetic material; and a plurality of propagate elements are disposed on the insulating layer to define paths beneath which the bubbles move. Those bubbles are moved in the film of magnetic material in response to another magnetic field that rotates in the plane of the film.
Typically, the propagate elements are shaped like asymmetric chevrons. They have a relatively wide end and a relatively narrow end; and they lie along the path of propagation in an end-to-end fashion with each chevron's relatively narrow end being spaced apart from the next succeeding chevron's relatively wide end.
Also included in the bubble memory is a magnetic bubble detector which contains a magnetostrictive sensing element. In operation, bubbles are propagated under the sensing element in response to the rotating magnetic field whereupon the bubbles induce a resistance change into the sensing element. That resistance change then indicates the presence (or absence) of a bubble.
Now, in the above-described bubble memory, the ease with which a bubble moves from one end of a propagate element to the other end and then to the next succeeding propagate element is not uniform. In particular, movement of the bubble becomes quite difficult as it crosses the space between propagate elements.
Also in the above-described bubble memory, the magnitude of the resistance change that is induced by a bubble in the sensing element is quite small; and that resistance change lasts for only a relatively short time. Thus, sensing such resistance change is quite difficult.
Accordingly, a primary object of the invention is to provide a method of operating a magnetic bubble memory system which improves the ease with which a bubble moves from one propagate element to another.
Another object of the invention is to provide a method of operating a magnetic bubble memory system which improves the ease with which a bubble is detected in a bubble detector.